Watermarking of video signals (that is, the embedding of some identifiable code, pattern or feature within the video signal) is known, and can be used to identify the source of a video signal or the signal's processing history, for example. It is also known to watermark a video signal as part of an encoding process, that is, to embed a watermark in the encoded signal, whether or not the source signal was already watermarked. Watermarking can also be regarded as imprinting a signal with an identifiable watermarking pattern. Throughout the remainder of this specification the term watermarking pattern will be used to encompass any such identifiable pattern, code or feature suitable for watermarking purposes.
Forensic tracking watermarks can form the basis for highly flexible and transparent copyright protection systems. For example, according to the watermark embedded in a signal, certain actions with that signal may be permitted (such as the recording of a watermarked movie on the storage device of a personal video recorder (PVR) or export of the movie to a user's portable player), whilst others denied (such as subsequent distribution of a received movie over a peer-to-peer network).
In general, video watermarking can be performed on baseband (uncompressed) or compressed video streams. Although the operations involved in baseband watermarking are generally simpler, the high data rates mean that the process either requires dedicated hardware or fast general-purpose processors. In contrast, the data rates for compressed domain watermarking are lower, but the complexity of parsing the bit-stream results in dedicated hardware or fast processors again being required. Thus, in either case, dedicated hardware or significant processor resources have in the past been necessary for video watermarking. Such dedicated hardware and/or the requisite processor resources have previously not been incorporated in consumer devices such as digital video recorders (DVRs), which are also known as personal video recorders (PVRs). These are devices that can record video without videotape to a digital storage device (typically a hard-drive-based storage medium), and include set-top boxes and software for personal computers. In other words, they permit capture and playback of video signals. Typically, current DVRs comprise limited processing resources and a dedicated encoder (such as a single encoder chip). Clearly, it would be problematic, if not impossible, to upgrade existing DVRs to increase their processing capabilities and to include additional hardware to enable them to watermark video signals.
A problem with certain known watermarking techniques is that it is possible to remove the watermark, for example by decompressing a watermarked encoded signal, and then re-compressing.